As is well-known, the low-temperature brittle fracture of steel is one of the most dangerous failures of a steel structure, the steel material features a brittle fracture at low temperature, and generally the steel and iron material has the following features when the brittle fracture occurs: (1) the operating stress born in fracture is lower than the yield limits; (2) once the brittle fracture occurs, it spreads at a very high speed (2000 m/s or higher); (3) the fracture is flat and straight, the reduction of area is small, and there is no macroscopic deformation feature on the exterior appearance; and (4) the appearance of fracture is generally an intergranular fracture. Once the brittle failure occurs, there will be significant losses, for example, in the World War II, there were about 1000 Liberty ships having brittle fractures.
Therefore, to continuously improve the low-temperature plasticity of the material becomes a research and test hotspot. At present, there are mainly two types of steel and iron materials widely used at low temperature. One type is low-carbon martensite low-temperature steel which is mainly 3.5% Ni, 5% Ni and 9% Ni steels. This type of steel plate can meet requirements on properties, but is expensive due to the high content of nickel; the other type is austenite low-temperature steel which mainly includes steel grades such as AISI304, 304LN, 316, 316LN and 310, and its chemical components are shown in table 1; this type of steel grade is low in low-temperature strength; although the low-temperature strength of the steel grades 304LN and 316LN is improved to certain extent by means of nitrogen strengthening, this type of steel is likely to have martensitic phase transformation that generates magnetism and stress. Consequently, the two types of steel described above have disadvantages that are insurmountable technically and economically.
TABLE 1Chemical components of commonly-used low-temperature steelChemical component (wt. %)Serial numberCrNiCSiMnSPAustenite30418-20 8-120.03——≤0.03≤0.03steel(00Cr18Ni9)310s24-2619-220.081.5—≤0.03≤0.03(Cr25Ni20Si)31616-1810-140.08——≤0.03≤0.03(Cr18Ni12Mo2Ti)316L16-1810-140.03——≤0.03≤0.03(00Cr17Ni12Mo2Ti)32117-19 9-120.08——≤0.03≤0.03(1Cr18Ni9Ti)Nickel3.5 Ni—3.25-3.75≤0.15——≤0.005≤0.02steel5 Ni—4.75-5.25≤0.15——≤0.005≤0.029 Ni—8.5-9.5≤0.130.15-0.4≤0.9≤0.04≤0.035